1. Field of the Invention
The present invention relates to a remote terminal apparatus of a programmable controller (hereinafter referred to as “PLC”), particularly to a building block type remote terminal apparatus in which an input and output unit (hereinafter referred to as I/O unit) can arbitrarily be added.
2. Description of the Related Art
There is well known a remote terminal apparatus connected to a PLC through a fieldbus, particularly a building block type remote terminal apparatus that includes one communication unit and at least one I/O unit capable of communicating with the communication unit through a serial bus, and in which an I/O unit may arbitrarily be added.
As this kind of building block type remote terminal apparatus, a building block type remote terminal apparatus with back plane and a building block type remote terminal apparatus without back plane are well known. In the building block type remote terminal apparatus with back plane, each I/O unit is attached to a conductive pattern laid on the back plane through a connector. The building block type remote terminal apparatus with back plane has an advantage that the communication can be continued without decoupling the serial bus line even in the case where the I/O unit is broken or detached. At the same time, the serial bus line having a length corresponding to the maximum number of connected I/O units is required on the back plane irrespective of the number of connected I/O units, and accordingly, the building block type remote terminal apparatus with back plane has a drawback that the long serial bus line abstracts the space saving.
On the other hand, in the building block type remote terminal apparatus without back plane, a conductive pattern which becomes a part of the serial bus line is laid outside a housing of each I/O unit, and both ends of the partial bus line lead out from right and left side faces of the housing. A set of serial buses is formed after the plural I/O units are connected to one another. Thus, the building block type remote terminal apparatus without back plane has an advantage that a wasted space is not generated, because the length of the serial bus line is set according to the number of connected I/O units. At the same time, when one of the set of I/O units is broken and removed, the serial bus is decoupled, which causes the drawback that the communication can not be continued.
Therefore, there is well known an I/O unit in which the whole of the I/O unit is divided into a base block including a serial bus line portion and a circuit block with terminal support including a circuit board and a input and output terminal support. The I/O unit having the two-divided configuration has an advantage that only the circuit block with terminal support is detached while the serial bus is not decoupled even if the break-down is generated in the circuit board. However, even in this case, in order to replace the circuit block with terminal support, there is a drawback that the wiring connected to the terminal support is laid again.
Recently there is proposed an I/O unit has the configuration in which the whole is divided into three by dividing the circuit block with terminal support into a main-body block including a communication control circuit and an input and output control circuit and a terminal block including a terminal support (refer to, for example, URL of a page explaining “X20 System” which is a product of B&R company: http://www.br-automation.com/cps/rde/xchg/SID-OA2B820A-4D98584C/br-automation_com/hs.xsl/cookies_allowed.htm?caller=556—5358_ENG_HTML.htm).
In the I/O unit having the three-divided configuration, the coupling is released between the terminal support block and the main-body block, and the coupling is released between the main-body block and the terminal support block. Therefore, the I/O unit having the three-divided configuration has an advantage that only the main-body block can easily be replaced while the terminal support wiring remains in the connected state.
FIG. 18 shows a view for explaining the conventional network. Referring to FIG. 18, the numeral 60 designates a tool placed on a network, the numeral 61 designates an upper communication, the numeral 62 designates a communication unit, and the numeral 63 designates an I/O unit. As shown in FIG. 18, the communication unit 62 includes an MPU 621, and the MPU 621 is connected to an I/O MPU 631 included in each I/O unit through an internal serial bus 64. In FIG. 18, the numeral 632 designates a setting switch built in the I/O unit 63.
However, in the conventional I/O unit 63 having the three-divided configuration, various pieces of information (various setting values and the like) stored in each I/O unit 63 is stored by the setting switch 632 (for example, DIP switch) of each I/O unit or the tool 60 connected to the upper communication 61. For example, when the I/O unit is replaced due to the failure of the I/O unit, the setting switch 632 is manually changed to the newly replaced I/O unit, or the data is downloaded from the tool 60 through the network.
According to the above technique, in replacing the I/O unit, the setting of switch of the replacement target unit is changed, or the tool is started up to download the stored setting value, which results in a long system down time during the unit replacement.
Because the setting of the I/O unit is manually downloaded, there might be generated a human-induced mistake such as an operation mistake of the setting switch 632. The problem is not limited to the case where I/O unit of the remote terminal apparatus is divided into three, but the problem is also generated in the case where the whole of the I/O unit is divided into the base block including the serial bus line portion and the circuit block with terminal support including the circuit board and the input and output terminal support.
In view of the foregoing, an object of the invention is to be able to perform the setting without using any tool to the newly replaced I/O unit to shorten the down time when the I/O unit is replaced during the current-conducting state or during the down state, in the I/O unit of the remote terminal apparatus in which the miniaturization and low-profile are developed.
Another object of the invention is to be able to securely prevent the human-induced mistake such as the operation error of the setting switch by setting the I/O unit without using any tool.
Other and further object, action, and effect of the invention will become manifest to those skilled in the art upon making reference to the following description.